I missed the original post on this or would have commented sooner.
Being a speech user for computers and a lot of other devices I'm fairly familiar
with current speech systems as well as systems used over the past 20 or so
years. I also am involved both with blind clients and a number of internet
lists composed of blind computer users and have come across no user complaints
concerning auditory problems with digital speech.
If for the moment we set aside the probability that there is at least some
auditory involvement with dyslexia, we should then consider which speech system
is being used. Treditionally lpc was used for the production of speech because
it took little memory compaired to digital speech. In recent years dedicated
speech synthesizers have been replaced by the use of sound cards. Some of these
systems use digital speech and some still rely on lpc. As sound card use has
become more popular with drivers such as DEC32 access blind users are finding
that they prefer to go back to dedicated speech synthesizers. In part this is
because of the poor responsiveness of sound cards and in part it is because of
poorer speech quality.
I believe that the research group at the American Foundation for the Blind has
begun looking at speech synthesis systems rather than only providing reports on
screen access programs. Listening to compressed or synthesized speech is a bit
tiring and it has been my experience that speech produced with a sound card is
particularly tiring because of background sound associated with the speech.
Although the speech produced by dedicated synthesizers may not be as clear or
human sounding as that producable by sound cards in many cases, I find it easier
to listen to for extended periods. It also often helps if you use a larger
speaker than that provided by synthesizers. Plugging your sound card into a
stereo may make a world of difference in the ease with which you can listen to
speech even though mistakes made by the synthesizer's chip programming will
become more apparent.
Tom
Tom Brennan, CCC-A/SLP, RHD
web page http://titan.sfasu.edu/~g_brennantg/sonicpage.html